© 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Chapter 20 Microbial Diseases of the Nervous System and Eyes

Structure of the Nervous System Divided into two parts –Central nervous system (CNS) –Peripheral nervous system (PNS) © 2012 Pearson Education Inc.

Figure 20.1 The nervous system-overview

Structure of the Nervous System Composed of the brain and spinal cord –Brain has several main parts –Cerebrum controls voluntary muscles, perception, and “thinking” –Cerebellum controls many involuntary body movements –Brain stem controls breathing, heart rate, blood pressure –Spinal cord – Extends from the brain stem to the lumbar region © 2012 Pearson Education Inc.

Structure of the Nervous System Structures of the Peripheral Nervous System –Nerves transfer commands from CNS to muscles and glands –Cranial nerves extend from brain through holes in the cranial bones –Spinal nerves extend from spinal cord through vertebral gaps –Three types of nerves –Sensory nerves – carry signals toward the CNS –Motor nerves – carry signals away from the CNS –Mixed nerves – carry signals toward and away from the CNS © 2012 Pearson Education Inc.

Structure of the Nervous System Cells of the Nervous System –Two basic cell types –Neuroglia –Provide support, insulation, nutrients; phagocytize microbes –Neurons –Carry nerve impulses –Nucleus lies in a region called the cell body –Ganglion is collection of many neurons’ cell bodies –Dendrites and axons extend from the cell body © 2012 Pearson Education Inc.

Structure of the Nervous System Portals of Infection of the Central Nervous System –CNS is an axenic environment –It has no normal microbiota –Pathogens may access the CNS several ways –Breaks in the bones and meninges –Medical procedures –Travel in peripheral neurons to the CNS –Infect and kill cells of the meninges, causing meningitis © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Bacteria cause disease in two ways –Infect cells of the nervous system –Meningitis –Leprosy –Bacteria growing elsewhere release toxins that affect neurons –Botulism –Tetanus © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Bacterial Meningitis –Signs and symptoms –Sudden high fever and severe meningeal inflammation –Encephalitis can result in behavioral changes, coma, and death –Can develop rapidly © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Bacterial Meningitis –Pathogens and virulence factors –Five species cause 90% of bacterial meningitis cases –Neisseria meningitidis –Streptococcus pneumoniae –Haemophilus influenzae –Listeria monocytogenes –Streptococcus agalactiae © 2012 Pearson Education Inc.

Figure 20.2 Diplococci of Neisseria meningitidis

Figure 20.3 Cells of Streptococcus pneumoniae

Figure 20.4 The pleomorphic bacili of Haemophilus influenzae Pleomorphisms

Figure 20.5 Listeria-overview

Bacterial Diseases of the Nervous System Bacterial Meningitis –Pathogenesis –S. agalactiae acquired during birth –Listeria transmitted via contaminated food –Other species transmitted via respiratory droplets –Epidemiology –S. pneumoniae present in throat of 75% of humans –Not spread by casual contact –Meningococcal meningitis can become epidemic © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Bacterial Meningitis –Diagnosis, treatment, and prevention –Diagnosis based on symptoms and culturing of bacteria from CSF –Treated with intravenous antimicrobial drugs –Vaccines available for S. pneumoniae, H. influenzae type b, and N. meningitidis –Individuals at risk for listeriosis should avoid high- risk foods © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Hansen’s Disease (Leprosy) –Signs and symptoms –Tuberculoid leprosy – nonprogressive –Lepromatous leprosy – progressive tissue destruction –Pathogen and virulence factors –Mycobacterium leprae is the causative agent –Gram-positive bacillus with mycolic acid in cell wall –Pathogenesis –M. leprae grows best in cooler regions of the body –M. leprae can live inside infected cells for years © 2012 Pearson Education Inc.

Figure 20.6 Lepromatous leprosy

Bacterial Diseases of the Nervous System Hansen’s Disease (Leprosy) –Epidemiology –Transmitted by person-to-person contact or breaks in the skin –Diagnosis, treatment, and prevention –Diagnosis based on the signs and symptoms –Confirmed by presence of acid-fast bacilli in samples –Treated with multiple antimicrobials –BCG vaccine provides some protection © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Botulism –Signs and symptoms –Caused by intoxication from ingested toxin – Three forms –Foodborne botulism –Infant botulism –Wound botulism –Pathogen and virulence factors –Clostridium botulinum is the causative agent –Different strains produce one of seven neurotoxins © 2012 Pearson Education Inc.

Figure 20.7 Botulism toxin-overview

Bacterial Diseases of the Nervous System Botulism –Epidemiology –~50 cases of foodborne and wound botulism per year in U.S. –Infant botulism most common form in U.S. –Diagnosis, treatment, and prevention –Three approaches to treatment –Washing of intestinal tract to remove Clostridium –Administration of botulism immune globulin –Treatment with antimicrobial drugs –Prevented by destroying endospores in contaminated food © 2012 Pearson Education Inc.

Bacterial Diseases of the Nervous System Tetanus –Signs and symptoms –Lockjaw –Spasms and contractions may spread to other muscles –Pathogen and virulence factors –Clostridium tetani is causative agent –Produce neurotoxin called tetanospasmin © 2012 Pearson Education Inc.

Figure 20.8 A patient with tetanus

Figure 20.9 Tetanus toxin-overview

Bacterial Diseases of the Nervous System Tetanus –Pathogenesis –Can acquire through break in skin or mucous membrane –Distance of infection from CNS determines incubation period –Epidemiology –Mortality rate is ~50% if left untreated –Diagnosis, treatment, and prevention –Diagnosis based on characteristic muscle contraction –Treated with passive immunotherapy, antimicrobials, active immunization –Vaccine available against tetanus © 2012 Pearson Education Inc.

Viral Diseases of the Nervous System Viruses more readily cross the blood- brain barrier Occur more frequently than bacterial and fungal infections Include meningitis, polio, rabies, and encephalitis © 2012 Pearson Education Inc.

Viral Diseases of the Nervous System Viral Meningitis –Signs and symptoms –Similar to those of bacterial meningitis –Usually milder than those of bacterial or fungal meningitis –Pathogens and virulence factors –90% of cases caused by viruses in the genus Enterovirus –Pathogenesis –Damage to cells in the meninges triggers meningitis © 2012 Pearson Education Inc.

Viral Diseases of the Nervous System Viral Meningitis –Epidemiology –More common than bacterial and fungal meningitis –Spread via respiratory droplets and feces –Diagnosis, treatment, and prevention –Diagnosed by characteristic signs and symptoms in the absence of bacteria in the CSF –No specific treatment exists © 2012 Pearson Education Inc.

Viral Diseases of the Nervous System Poliomyelitis –Signs and symptoms –Asymptomatic infections – almost 90% of cases –Minor polio – nonspecific symptoms –Nonparalytic polio – muscle spasms and back pain –Paralytic polio – produces paralysis –Pathogen and pathogenesis –Poliovirus is the causative agent –Transmitted most often by drinking contaminated water © 2012 Pearson Education Inc.

Figure A hospital ward filled with “ iron lungs ”

Figure Poliomyelitis-overview

Table 20.1 Comparison of Polio Vaccines

Viral Diseases of the Nervous System Rabies –Signs and symptoms –Characteristic neurological signs if virus reaches CNS –Pathogen and virulence factors –Rabies virus –Pathogenesis –Transmitted via bite or scratch from an infected animal –Virus replicates in muscle cells and then moves into neurons © 2012 Pearson Education Inc.

Viral Diseases of the Nervous System Rabies –Epidemiology –Zoonotic disease –Diagnosis, treatment, and prevention –Diagnosis by unique neurological symptoms –Postmortem detection of Negri bodies in the brain –Treated with human rabies immunoglobulin, vaccine injections, and cleansing infection site –Prevented by controlling rabies in domestic animals © 2012 Pearson Education Inc.

Figure Predominant wildlife reservoirs for rabies in the U.S. Skunk Fox Raccoon

Figure Negri bodies Negri bodies

Viral Diseases of the Nervous System Arboviral Encephalitis –Arboviruses are arthropod-borne viruses –Transmitted via blood-sucking arthropods (e.g., mosquitoes) –Mosquito-borne arboviruses can cause arboviral encephalitis –As zoonotic diseases, they rarely affect humans –Arboviruses usually cause mild, coldlike symptoms –Can cause if cross the blood-brain barrier © 2012 Pearson Education Inc.

Table 20.2 Characteristics of Arboviral Encephalitis Diseases and Viruses in the United States

Figure Togaviruses

Figure Transmission of six encephalitis arboviruses Domestic fowls Wild birds Mosquitoes are vectors. Humans can be infected via mosquito bites. Small mammals are hosts for VEE and California viruses only. Horses, and rarely other domestic mammals are hosts for equine viruses. Birds are hosts for all six encephalitis arboviruses. Encephalitis arboviruses can overwinter inside mosquito eggs.

Figure Human West Nile virus encephalitis in the United States Time (months/years) Reported cases Annual deaths Number of reported cases (299) (9) (264) (84) (86) (43) (30) (124)

Viral Diseases of the Nervous System Arboviral Encephalitis –Diagnosis based on signs and symptoms –Confirmed by presence of arbovirus-specific antibodies in CSF –Treatment is supportive –Prevention involves limiting contact with mosquitoes –Use netting and insect repellents –Eliminate stagnant water –Vaccines for horses available against EEE, WEE, VEE, and WNV © 2012 Pearson Education Inc.

Mycoses of the Nervous System –Mycoses are fungal diseases –Spread from the lungs to the CNS via the blood –Mushroom toxins can produce hallucinations and neurological problems –May also produce fungal meningitis © 2012 Pearson Education Inc.

Mycoses of the Nervous System Cryptococcal Meningitis –Signs and symptoms –Similar to those of bacterial meningitis –Pathogen and virulence factors –Cryptococcus neoformans is causative agent –Two variants of the yeast found worldwide –Resists phagocytosis by defensive cells © 2012 Pearson Education Inc.

Mycoses of the Nervous System Cryptococcal Meningitis –Pathogenesis and epidemiology –Infections follows inhalation of spores or dried yeast cells –Occurs in terminal AIDS patients and in transplant recipients –Diagnosis, treatment, and prevention –Diagnosed by detection of fungal antigen in CSF –Treated with intravenous antifungal drugs © 2012 Pearson Education Inc.

Protozoan Diseases of the Nervous System Protozoan infections of the nervous system are rare Two diseases caused by protozoa –African sleeping sickness –Meningoencephalitis © 2012 Pearson Education Inc.

Protozoan Diseases of the Nervous System African Sleeping Sickness –Signs and symptoms –Three clinical stages –Site of bite becomes lesion –Parasites in the blood create fever, lymph node swelling, and headache –Meningoencephalitis results when protozoa invade the CNS –Pathogen and virulence factors –Caused by Trypanosoma brucei –Evades immune system by changing surface glycoproteins © 2012 Pearson Education Inc.

Figure The life cycle of Trypanosoma brucei Trypomastigotes reproduce by binary fission, becoming epimastigotes in midgut of tsetse fly. Epimastigotes migrate to salivary glands. Glossina (tsetse fly) Trypomastigotes are ingested by tsetse fly during blood meal. Some trypomastigotes invade central nervous system. Trypomastigotes multiply by binary fission in bodily fluids, including blood, lymph, and spinal fluid. Trypanosoma epimastigote matures into infective trypomastigote within salivary gland of tsetse fly. Tsetse fly injects trypomastigotes while feeding. Trypomastigotes are carried via bloodstream to other sites.

Protozoan Diseases of the Nervous System African Sleeping Sickness –Diagnosis, treatment, and prevention –Diagnosed by microscopic observation of trypanosomes in blood, lymph, or spinal fluid –Alternatively, tissue biopsy may be done –Treatment based on disease stage –Insecticide application can help reduce occurrence © 2012 Pearson Education Inc.

Protozoan Diseases of the Nervous System Primary Amebic Meningoencephalopathy –Signs and symptoms –Same as those of meningitis and encephalitis caused by other microbes –Pathogen, pathogenesis, and epidemiology –Caused by Acanthamoeba and Naegleria –Enter host through abrasions on the skin or the eyelid or by inhalation of contaminated water –Diagnosis, treatment, and prevention –Drugs have limited success –Prevented by avoiding possibly contaminated water supplies © 2012 Pearson Education Inc.

Prion Disease A prion is an infectious protein Spongiform encephalopathies –A class of diseases that includes scrapie and mad cow disease –Leave the brains of victims full of holes –Humans can contract by eating meat from infected cattle © 2012 Pearson Education Inc.

Prion Disease Variant Creutzfeldt-Jakob Disease –Signs and symptoms –Insomnia, weight loss, and memory failure –Progressive worsening of muscle control –Pathogen, pathogenesis, and epidemiology –Caused by abnormal form of prion –Prions may remain formant for many years –Diagnosis, treatment, and prevention –Diagnosed by characteristic signs and symptoms –Confused with other forms of dementia in elderly –No treatment is available –Prevented by avoiding prion contaminated meat © 2012 Pearson Education Inc.

Microbial Diseases of the Eye –Senses are important part of the nervous system –Vision comprises almost half of the function of the cerebrum © 2012 Pearson Education Inc.

Figure The eye Extension of dura mater Optic nerve Sclera Retina Cornea Conjunctiva

Microbial Diseases of the Eye Trachoma –Pathogen, pathogenesis, and epidemiology –Caused by Chlamydia trachomatis –Multiplies in the conjunctiva –Results in discharge and deformed eyelids –Can lead to blindness –Typically affects children –Diagnosis, treatment, and prevention –Diagnosed by identifying bacteria at site of infection –Treated with antimicrobials and surgery © 2012 Pearson Education Inc.

Figure An eyelid afflicted with trachoma

Microbial Diseases of the Eye Other Microbial Diseases of the Eye –Bacterial infections of skin and reproductive tract can affect the eyes –Sties –Infections of the sebaceous glands near the eye –Ophthalmia neonatorum –Inflammation of the conjunctiva and cornea of a newborn –Conjunctivitis –Inflammation of the conjunctiva –Keratitis –Inflammation of the cornea © 2012 Pearson Education Inc.